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TED STATES DEPARTMENT OF AGRICULTURE 

E BULLETIN No. 992 Mm* 



Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 



JZys^ru 



Washington, D. C. 



November 4, 1921 



WALNUT HUSK-MAGGOT. 1 

Bv Feed E. Brooks, Entomologist, Fruit Insect Investigations. 



CONTENTS. 



Pago. 

Introduction ± — 1 

Brief description of insect and in- 

o 

jury 

Synonymy 

Distribution 

Food plants 3 



Description of life stages 

Activities of the flies 

Nature of injury 

Natural enemies 

Methods of control 



INTRODUCTION. 

The larva of the walnut husk-maggot has long been known to 
persons who in autumn have engaged in hulling the nuts of our 
native black walnut (Juglam nigra). Soon after the nuts drop, a 
large percentage of them are frequently found with the hulls black- 
ened and slimy within and containing multitudes of whitish mag- 
gots which move actively through the soft pulp. Such infested nuts 
are disagreeable to handle, and in hulling the husk sticks to the 
inner shell, leaving it dirty and unattractive in appearance (PI. IV. 
d). Inasmuch as the fruit of the black walnut was not important 
commercially in the past this insect did not attract especial attention, 
and very few persons, even of those who were familiar with the mag- 
gots in the walnuts, ever saw the parent fly. If seen, it was probably 
seldom regarded as being in any way connected with the disgusting 

~Rhagoletis ^avis Loew ; order Diptera, family Trypetidae. A closely allied species. 
Rhagoletis juglanMs Cresson, has been recorded ns attacking the nuts of Juglms rupestns 
and J regia in Arizona and Texas. Several members of the same genus have attracted 
considerable attention in North America on account of the destructiveness of the larvae 
to various kinds of fruit. R. pomonella Walsh, known commonly as the apple maggot 
or railroad worm, is an important pest of apples in the northern part of the United 
States and Canada. Two species, 7?. cingulata Loew and R, fwusta O. S., attack cherries 
over practically the same region, while R. nlicola Doane frequently injures currants and 
gooseberries in the Northwestern States. 
55813°— 21 



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Monograph 



2 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE. 

condition of the nuts. It was not until an interest developed in cer- 
tain places in the East in growing the Persian or English walnut 
(Juglans regia) commercially that a demand arose for information 
regarding this pest. When the Persian walnut trees planted in the 
East began to fruit, these maggots attacked the nuts and practically 
ruined very promising crops in several localities. The injury to Per- 
sian walnuts and the fact that the eastern black walnut, one of the 
favorite food plants of the species, is becoming of increasing im- 
portance from the standpoint of nut production, have led to the in- 
vestigation described herein. The project is not yet completed, but 
the outstanding features of the life history and habits of the insect 
are now known. Further studies of the species, particularly along 
the lines of control, are under way. 

BRIEF DESCRIPTION OF INSECT AND INJURY. 

The adult of the walnut husk-maggot is a two-winged fly about 
the size of the common house fly. The flies appear on the walnut trees 
tit the time the nuts are approaching maturity and lay clusters of 
white eggs in punctures made in the husk with their sharp ovipositor 
(PI. Ill, e) or in breaks which they may find in the husk of the nuts 
(PI. II, b, c, d). Apparently no eggs are deposited in the nuts after 
they drop. The eggs soon hatch and the resultant maggots rapidly 
convert the green tissue of the husk into black pulp. After attain- 
ing full growth the maggots enter the ground and pupate, there 
being onty one generation of the flies annually. 

SYNONYMY. 

The following data covering the synonymy of .the species were fur- 
nished by Mr. B. A. Porter, of the Bureau of Entomology : 

Try pet a suavis Loew, 1S62, in Monogr. Dipt. N. Amer., pt. 1, p. 75. 
Acidia ,sii<tris Loew, 1873, in Monogr. Dipt. N. Amer. pt. 3, p. 235. 
Bhagoletis suavis (Loew). 1899, in Coquillett, Jour. N. Y. Ent. Soc, 
v. 7. p. 260. 

DISTRIBUTION. 

This fly probably occurs pretty generally over the natural ranges 
of the black walnut and the butternut (Juglans cinerea). In 1862 
Osten-Sacken 2 gave its distribution as the "Middle States."" In 
1902 Babb 3 reared the fly from black walnut at Amherst, Mass. 
Washburn, 4 in 1905, listed the species among the flies of Minnesota ; 

2 LoeWj H. monogkaphs of the diptera of noeth amekica (ed. by R. Osten-Sacken) , 
pt. 1, p. 75. Washington, D. C. 1862. 

3 Babe, G. F. note on rhagoletis suavis lw., with a description of the larva 
and puparium. In Ent. News, v. 13, no. 8, p. 242. 1902. 

4 Washburn, F. L. diptera of Minnesota. . Minn. Agr. Exp. Sta. Bui. 93, p. 118. 
1905. 

UBHARY OF CONQKI88 | 
006UMENT& DIVISION 



£f£> ^>-> * WALNUT HUSK-MAGGOT. 3 

and Banks, 5 in 1912, reared flies from butternuts at Plummers Island. 
Md. There are specimens in the United States National Museum 
from West Willow and Allegheny, Pa., and Dr. J. M. Aldrich, of 
the Museum, has in his personal collection specimens from Blue 
Ridge Summit. Pa., and La Fayette, Ind. During the present in- 
vestigation the writer has collected or otherwise obtained specimens 
from the following localities: Boston, Mass.; Wallingford, Conn.; 
Lockport, N. Y.; West Willow and Washington Heights, Pa.; Co- 
lumbus, Ohio ; New Windsor, Md. ; Washington, D. C. ; and French 
Creek and other localities in West Virginia. 

FOOD PLANTS. 

The walnut husk-maggot has been known to attack commonly the 
husks of the black walnut (Juglans nigra) and the butternut (•/. 
cinerea) . The writer has reared adults from the husks of the Persian 
walnut (J. regia) and Japanese walnut (-/. sieboldiana). Of the 
foregoing hosts the black walnut and Persian walnut are preferred 
to the others, probably on account of the thicker husks. 

DESCRIPTION OF LIFE STAGES. 

THE EGG. 

The egg (PI. II, b, <?, d) is white, banana-shaped, distinctly curved, 
0.9 to 1 mm. in length by 0.2 mm. in width, one end tapering gradu- 
ally to a rounded point, the other end tapering more abruptly and 
ending in a minute but distinct spur or pedicle. The eggs are placed 
in masses compressed closely together (PI. II, b, c, (!) in oviposition 
punctures extending 2 mm., more or less, beneath the skin of the 
nuts. The female will oviposit freely in any fresh puncture which 
she may find in the skin made otherwise than with her ovipositor. 
Small punctures made experimentally in the husk with a sharp point 
usually were found promptly by the females and filled with eggs. 
In some cases such punctures would be packed with eggs and the 
flies would continue to oviposit on the surface until a small mound 
of eggs covered the opening in the skin (PI. II, d). One artificial 
puncture in a black walnut was. found to contain 186 eggs and several 
punctures made with the ovipositor were found to hold upwards of 
CO eggs each. The eggs apparently hatch in from 7 to 10 days. 

Oviposition takes place only in the green part of the husk, but 
after the maggots hatch and begin to feed the point of attack soon 
shows as a black spot on the surface (PI. IV, a). This spot increases 
rapidly in size as the burrows of the maggots penetrate the tissues 

: ' Banes, Nathan, the structure of certain dipterous i.aiiy.u with particular ref- 
erence to those, in human foods. U. S. Dept. Agr., Bur. Ent., Tecli. Ser. Bui. 2'1, 
1>. 32. 1912. 



4 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE. 

beneath. Persian walnuts on the trees will often turn black from 
this cause during a period of only a few days. Quite often the first 
external evidence of the feeding of the larva? within a nut will be a 
slight seepage of dark juice from the oviposition wound, which will 
flow down and stain the skin of the nut (PI. IV, b). 

THE LARVA. 

The larva, or maggot (PL II, e, /,' PI. IV, c), is white or creamy 
white, and is not stained by the dye-like, semiliquid matter in which 
it feeds. The dark-colored contents of the alimentary canal, how- 
ever, give to the immature maggots a brownish appearance. When 
full grown the}' average 10 mm. in length by 2 mm. in width. The 
maggots are active and move about rapidly, using in locomotion their 
Iavo anal hooks. The}' often remain in the walnut husk until severe 
freezing weather occurs, but take advantage of warm periods in the 
late autumn to leave the nuts and enter the ground a short distance 
for pupation. 

THE PUPA. 

The pupa (PI. II, g, h) is formed by the shrinkage of the larva 
and is pale yellow, cylindrical, tapers slightly from the middle to- 
ward the ends, and is 5 mm. in length by 2.5 mm. in width. There 
are 11 plainly visible segments, the intersegmental grooves being 
shallow but distinct. Each end bears a pair of small, brownish 
tubercles and there is a rough, brown spot near one end where the 
larval head was retracted. In size, shape, and color the pupa re- 
sembles a grain of wheat (PI. II, h). The pupae are formed in the 
ground, anywhere from half an inch to several inches beneath the 
surface, and the winter is passed in this stage. Most, of the flies 
issue the following summer, but a few pupa? hold over the second 
winter and the adults appear therefrom during the succeeding 
summer. 

THE ADULT. 

The adults of this insect vary considerably in size but average about 
7 mm. in length. With the exception of the eyes, heavy wing mark- 
ings, anterior margins of the abdominal segments, and bristle-like 
hairs, all of which are dark brown, the color is pale yellow. There 
is a lighter longitudinal line on each side of the thorax and the 
dorsal surface of the thorax is densely clothed with very short, 
yellowish hairs interspersed sparsely with long, stiff, dark-brown 
bristles. The head, sides, upper surface of the abdomen, and legs 
are covered more or less heavily with brown hairs. (PL III.) 

ACTIVITIES OF THE FLIES. 

The flies begin to issue from the ground at least as early as the 
middle of July in the latitude of West Virginia. In 1920 at French 



Sul. 992, U. S. Dept. of Agriculture 



Plate I. 




Bui. 992, U. S. Dept. of Agriculture. 



Plate i I 




a 






\ 




hm^ 




The Walnut Husk-Maggot. 

a, Genitalia of male and female husk-maggots, male on left; 6 and c, egg clusters in black walnuts 
exposed by cutting away the skin: d, egg cluster partly on 1 he surface of black walnut; e, larvae; 
/, larva escaping from a' black walnut; g, pupae; h, resemblance of pupae, above, and grains of 
wheat, below. All enlarged. 



Bui. 992, U. S. Dept. of Agriculture. 



PLATE III 




The Walnut Husk-Maggot. 

a, Flies of husk-maggot on black walnut; b, fly of husk-maggot much enlarged; c, female in the 
act of depositing eggs in a black walnut; d, female laying eggs and guarded by a male; e, female 
with ovipositor extended. All enlarged. 



Bui. 992, U. S. Dept. of Agriculture 



PLATE IV. 




The Walnut Husk- Maggot. 

, Black walnut showing discolored spot on skin made by husk-maggots mining within; 6, black 
walnut stained by juice flowing from oviposition scar; c, husk-maggots in Persian walnut: 
d, black walnuts with husk removed to show difference in hulling between sound and infested 
nuts; nut on the left sound, on the right infested. All about natural size. 



WALNUT HUSK-MAGGOT. 



Creek, W. Va., the first flies appeared in rearing jars on July 10, 
and on August 5 the first specimens were recognized definitely on 
the trees. Flies, apparently of this species, were seen on trees in both 
West Virginia and Pennsylvania several weeks earlier, but no 
specimens were captured and identification was not definite. Flies 
in rearing jars issued from July 16 to September 8, emergence cover- 
ing a period of 55 days. Table I shows the time of emergence of 40 
individuals in rearing jars. 

Table I. — Emergence of flies of walnut husk-maggot in rearing iars at 
French Creek, W. Va., in 1920. 



Date 


Num- 
ber of 
flies. 


Date. 


Num- 
ber ol 
flies. 


Date. 


Num- 
ber of 
flies. 


Date. 


Num- 
ber of 
flies. 


July 16.... 
17.... 
18.... 
19 

20. . . . 
21.... 
22.... 
23. . . . 
24. . . . 

26. . . . 
27. . . . 
28. . . . 
29. . . . 
30. . . . 


1 



2 

1 


1 




1 

n 






.lulv 31.... 

Aug. 1.... 

2 

3.'.'.'. 

4 

5 . . . . 

6 

7 

8 . 
9 

10.... 

11.... 

12 

13.... 

14.... 


1 
1 



1 



1 
1 
1 
1 



2 

1 



Aug. 15 

16... 
17... 
18... 
19... 
20... 
21... 
22... 
23... 
24... 
25... 
26... 
27... 
28... 


3 


2 
2 

s 



1 

1 
4 
4 
1 



Aug. 29... 

30... 

31... 
Sept. 1 . . . . 

2 

3.'.'.. 

i.... 

6.... 
7.... 

8.... 
9.... 

Total. . 




1 



1 



1 



40 



Apparently flies are present on the trees several weeks before ovi- 
position begins. At first they occupy the foliage chiefly, making 
short flights from leaf to leaf and resting quietly for long periods. 
During the preoviposition period, as well as later, they may be seen 
lapping at the leaves as though extracting food from deposits on the 
surface. As the time for the beginning of oviposition approaches 
the flies become more active, and both males and females show a 
tendency to gather about the nuts. The males habitually select cer- 
tain nuts on which an individual will take his stand and often remain 
for hours at a time awaiting the coming of the female, combating, 
meantime, other males that approach. When a male alights on a nut 
already tenanted by another male the original occupant attacks it and 
usually the two rear up on their hind legs, facing each other, and en- 
gage in a brief but animated bout, belaboring each other with their 
forelegs. Usually the original occupant is the victor and the would- 
be interloper flies away. 

A prick made in a walnut with a pin or other sharp point was sure 
to be found by a male, who, recognizing it evidently as a suitable 
place for the females to come to oviposit, would immediately begin 
standing guard over it. In one instance the writer pricked a dozen 
walnuts on the lower branches of a tree with the point of a small 
nail. Thereafter for several days a male was on guard at each of the 



6 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE. 

punctured nuts and females were observed frequently to visit these 
nuts, where copulation and oviposition took place. In approaching 
these nuts the females usually came by easy stages, flying and crawl- 
ing near the nut before alighting upon it. When the male would 
observe a female approaching he would become much excited, moving 
back and forth, whirling around, and raising and lowering the wings 
in rapid succession, but remaining near the puncture made with the 
nail point. On the arrival of the female upon the nut the male 
would usually back away from the nail puncture a short distance 
and there remain stationary, with wings elevated above the back,, 
watching the female intently. When the female would find the 
puncture and start to insert the tip of her abdomen into the opening 
for the purpose of depositing eggs, the male would spring upon her 
and copulation would take place. There would then follow alter- 
nating periods of oviposition and copulation, the male sometimes 
continuing mounted while oviposition was in progress, and sometimes 
dismounting but remaining near by. (PI. Ill, cl.) Frequently there 
would be four or five periods of each before the female would fly 
away. After this procedure the male was likely to continue on 
guard at the same place, for the nail pricks were visited frequently 
by ovipositing females. 

The flies were observed to be much more abundant on the lower 
than on the higher branches of trees, and there was a great differ- 
ence in the numbers of flies on individual trees of the same species. 
On a group of heavy-laden Persian walnut trees of the variety 
known as Hall, at West Willow, Pa., it was estimated that one fly 
was present for every two nuts on the trees. The variation in the 
numbers of flies on individual trees was followed by a corresponding 
abundance or scarcity of maggots in the nuts of each. 

Flies were observed to feed upon the juice that flowed from ovi- 
position scars and upon the naturally more or less gummy surface 
of the nuts. In feeding they would eject from the mouth a particle 
of clear liquid onto the surface and after working it over with the 
purselike, external mouthparts would swallow it again. 

NATURE OF INJURY. 

In native black walnuts the eggs of the husk-maggot fly are 
usually deposited so late in the season that the resultant maggots 
do not prevent the nuts from maturing and dropping normally. 
Thus, while apparently all the eggs are laid in nuts on the trees, 
the development of the maggots and the blackening of the husks 
which results from their feeding take place chiefly in fallen nuts. 
In Persian walnuts, however, eggs appear to be laid earlier in the 
development of the nuts. Bearing trees were observed in Maryland 
and Pennsylvania, a short time before the crop had ripened, on which 



WALNUT HUSK-MAGGOT. 7 

a large percentage of the husks of the nuts were blackened through- 
out and the surface covered with a gummy exudation from the mag- 
got injury within. Some of the infested Persian walnuts drop 
prematurely and others hang to the branches until after the 
sound nuts have fallen. In nuts that are attacked before maturing 
the development is arrested and the kernel becomes unfit for use. 
The injury is thus threefold, in that it impairs the quality of the 
kernel, causes the husk to stick to the shell in the hulling process, and 
blackens and soils the shell, making the huts unattractive for market. 

NATURAL ENEMIES. 

Only one parasite of the husk-maggot has been discovered. This 
is a hymenopterous species, Ayliaereta auripes Prov., reared from 
the puparia by Babb ( 6 ) at Amherst, Mass. The writer, on Sep- 
tember 8, 1920, found a small leaf-bug, determined by W. L. McAtee 
as a species of Lopidea, with its beak inserted through the skin of a 
black walnut sucking out the contents of a batch of fresh-laid husk- 
maggot eggs. An examination of the eggs showed that a number of 
them had been punctured and emptied by the bug. 

METHODS OF CONTROL. 

Experiments in controling the husk maggot with lead-arsenate 
sprays were conducted in 1920 in the Persian walnut groves of Mr. 
N". H. Baile, at New Windsor, Md., and of Mr. J. G. Push, at West 
Willow, Pa. Only a single application of the spray was made in each 
case. The grove of Mr. Baile consists of about a dozen seedling trees 
of various sizes, some of them about 30 years of age. At the time 
of the spraying all were bearing heavy crops of nuts. This grove 
was sprayed by means of a power sprayer on August 10, with 3 
pounds of lead-arsenate paste to 50 gallons of water. The grove of 
Mr. Push consists of 18 trees of named varieties, all of bearing age. 
The trees were producing heavily at the time the spray was applied. 
The spraying was done on August 9, using 1| pounds of lead-arsenate 
powder to 50 gallons of water. Two trees of the variety known as 
Rush, three of Hall, and two of Mayette were sprayed with the lead- 
arsenate solution to which enough molasses had been added to give 
the liquid a slightly sweetish taste. For treating the Rush grove a 
small hand sprayer mounted on a wheelbarrow was used (PI. I). 
The trees of both groves had borne the previous season, but the crops 
had been injured seriously by the attacks of the maggots. 

At the time the groves were sprayed the adults of the maggots 
were appearing on the trees and a close examination of the nuts in 
the Rush grove disclosed one batch of freshly laid eggs. After the 
spraying the Baile grove was not revisited until the nuts were almost 

Babb, G. F. op cit. 



8 



BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE. 



ripe. The Rush grove, however, was kept under close observation 
by Mr. Rush and the writer. The flies became very numerous on the 
trees of this grove for a period of a few days after the spray was 
applied and then decreased in numbers. 

Examination and counts of the nuts of the sprayed trees in the 
Baile grove just before the crop was gathered showed that 4 per 
cent of the nuts had been attacked by the maggots, whereas at least 
CO per cent of the crop had been destroyed by the maggots the pre- 
vious year. In the Rush grove it was estimated that the condition 
Avas 75 per cent better than the year before when no treatment was 
given. No Persian walnut trees were found near either the Baile or 
Rush groves that were suitable for use in checking up definite results 
of the spraying. However, a comparison of the sprayed nuts with 
those produced by the same trees the previous season and with those 
produced in other localities the same season, together with the known 
abundance of the flies that appeared early upon the sprayed trees, 
indicates decidedly beneficial results from the treatment. 

Flies confined in roomy wire-screen cages were observed to feed 
freely on sweetened water to which sufficient lead arsenate had been 
added to give the liquid a milky color. It must be admitted that 
these flies succumbed very slowly to the poison. Further tests of 
this treatment must be made before it can be recommended unre- 
servedly as an effective and sure method of control for this pest. 

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